Regression and its mechanisms after laser in situ keratomileusis in moderate and high myopia

Objective: The purpose of the study was to evaluate the degree and mechanism of regression after laser in situ keratomileusis (LASIK) on moderate to highly myopic eyes during the first postoperative year, Design: A prospective, single-center, clinical trial. Participants: A total of 52 eyes of 38 patients were entered in the study; 47 eyes had complete data available at each postoperative visit. Intervention: The intervention was LASIK using the microkeratome to create an 8.5- to 9.0-mm diameter, 130- to 160-mu m-thick flap. A spherical midstromal multizone ablation (inner zone, 4.5 mm; outer zone, 5.5-6.0 mm) was then performed using the Summit OmniMed excimer laser (Summit Technology, Inc, Waltham, MA). The mean preoperative refraction was -14.02 diopters (D). Retreatment for undercorrection and regression was performed between postoperative months 3 and 6 on 13 eyes. Main Outcome Measures: Manifest spherical equivalent, mean central corneal power, and central corneal thickness were the parameters measured. Results: At 3 months, follow-up data were available on 47 eyes. The mean refractive regression was -1.07 D (7.6%) from the first week to the third month. During the first postoperative year, the mean regression of manifest spherical equivalent (MSE), increase in corneal power, and increase in corneal thickness were symmetric in magnitude and time course for the 34 eyes that did not require retreatment (-0.96 D, +1.03 D, and 15 mu m, respectively). Conclusion: Early regression of refractive effect after LASIK appears to be a consequence of an increase in corneal thickness associated with central corneal steepening. No evidence of progressive corneal ectasia was observed during the first year of follow-up. Longer follow-up is required to confirm these trends.